FIELD OF THE INVENTION
[0001] The present invention relates to polyimide laminate comprising thermoplastic polyimide
polymer, or thermoplastic polyimide film, and a method of manufacturing the polyimide
laminate. More particularly, the invention relates to the use of a thermoplastic polyimide
polymer featuring adhesive film-forming properties, distinguished thermal resistant
property, solid adhesion under low temperature, and low hygroscopic degree; or the
use of a thermoplastic polyimide film which is produced from this thermoplastic polyimide
polymer in a polyimide laminate which is applicable to the formation of a base film
of a coverlay film for producing flexible printed circuit boards (FPC); polyimide
laminate which consists of a laminate of layers of the above identified thermoplastic
polyimide film and nonthermoplastic polyimide film and is usable for bilateral adhesive
sheets, flexible copper coated laminated boards, or cover-lay film; and the invention
also relates to the method of manufacturing the polyimide laminate.
BACKGROUND ART
[0002] Recently, as a result of rapidly promoted functional capacity and down-sizing of
a variety of electronic apparatuses, there is a growing demand for further reduction
of the size and weight of electronic parts built therein. In particular, there is
a sharply growing demand for flexible printed circuit boards (hereinafter merely referred
to as FPC) for mounting a variety of electronic parts against conventional rigid printed
circuit boards.
[0003] Basically, any of conventional flexible printed circuit boards has such a structure
in which "cover-lay film" is coated on the surface of circuit patterns formed on a
soft and thin base film. At present, in order to satisfy essential characteristics
such as mechanical characteristic, electrical characteristic, chemical resistant property,
thermal resistant property, and resistance to environmental condition normally being
required for the base film and the cover-lay film, polyimide film has been used most
extensively.
[0004] Sequential processes for manufacturing such a conventional flexible printed circuit
board comprise the following: Initially, a flexible copper-coated laminate (FCCL)
is formed by laminating a base polyimide film and a copper foil. Next, a resist pattern
is formed on the produced conductor via a screen printing process or a photo-resist
process, and then a circuit pattern is formed by executing an etching process. Finally,
a cover-lay film is laminated on the surface of circuits of the film having the circuit
pattern formed therein. When executing the above sequential processes, either acrylic
adhesive agent or epoxy adhesive agent is mainly used for laminating the base film
with copper foil or laminating the cover-lay film on the surface of the built-in circuits.
[0005] Nevertheless, any of these conventional adhesive agents proved to be poor in the
thermal resistant property and yet contains high rate of hygroscopicity. In consequence,
physical properties of the produced flexible printed circuit boards such as the thermal
resistant property and dimensional stability are dependent on the physical properties
of the used adhesive agent, thus preventing the polyimide film being used for the
cover-lay film and the base film from fully exerting own distinct performance characteristic
in many cases. In association with the promotion of multiplied layers of flexible
printed circuit boards in recent years, there is a growing demand for bi-lateral adhesive
sheets having both surfaces of the base film coated with adhesive agent. However,
since either acrylic adhesive agent or epoxy adhesive agent is also used for producing
such a bilateral adhesive sheet, like the above case, polyimide film cannot fully
exert own distinct performance characteristic.
[0006] In order to laminate a cover-lay film on the surface of the built in circuits in
the course of manufacturing a flexible printed circuit board, it is a conventional
practice to execute those sequential processes including an initial step to adhere
either of the above adhesive agents onto the surface of a polyimide film, a next step
to process a cover-lay film having one-side surface adhered with the above adhesive
agent into a predetermined shape, a next step to superpose the formed cover-lay film
on the surface of circuits of the polyimide film having circuit patterns formed thereon,
a next step to correctly position them, and a final step to thermally bond them via
a pressing means. However, when applying either of the above-cited adhesive agents
in the course of executing the above processes, since perforation cannot be executed
after bonding the cover-lay film with the flexible printed circuit board, before bonding
the polyimide film, the conventional art has been obliged to perforate the cover-lay
film to provide through-holes or windows at terminals of circuits formed on the conductor
or at junctions connected to component parts.
[0007] On the other hand, not only difficulty is involved in properly perforating an extremely
thin cover-lay film, but working efficiency is also poor and it is costly because
the work for positioning the perforated cover-lay film at a predetermined position
of the flexible printed circuit board has conventionally and substantially been executed
via manual means. Furthermore, if there were too thin thickness of layer of adhesive
agent for bonding the cover-lay film, it may lead to the generation of void effect
between the flexible printed circuit board and the cover-lay film. Conversely, if
there were too thick layer of adhesive agent, it often causes the adhesive agent to
ooze itself into perforated domains to result in the faulty conductive effect.
[0008] US-A-5,096,998 discloses a reactive oligoimide which may serve as an adhesive for
bonding at least one layer or film to another layer preferably a flexible metallic
layer to a flexible layer of a polyimide in order to form a flexible multilayer metal-clad
laminate.
[0009] In order to fully solve the above problems, the invention has been achieved by way
of providing improved polyimide laminate comprising improved thermoplastic polyimide
polymer, or improved thermoplastic polyimide film, and an improved method of manufacturing
the polyimide laminate, which respectively feature distinct thermal resistant property
and wherein the adhesive agent layers comprising the thermoplastic polyimide polymer
are suitably usable for the formation of coverlay adhesive agent and layers of adhesive
agent for bonding a coverlay film or flexible copper-coated layers or bilateral adhesive
sheets each featuring distinct workability and adhesive property.
DISCLOSURE OF THE INVENTION
[0010] Essentials of the thermoplastic polyimide polymer used for the inventive polyimide
laminate for achieving the above object are exemplified in general formula (1) shown
below; wherein Ar
1, Ar
2, Ar
4, and Ar
6 respectively represent divalent organic radicals; Ar
3 and Ar
5 respectively represent quadrivalent organic radicals. Symbolic characters 1, m, and
n respectively represent positive integer of 0 or 1 or more than 1, wherein the sum
of 1 and m is 1 or more than 1, and wherein symbolic character t represents positive
integer of 1 or more than 1.
[0011] The thermoplastic polyimide polymer used for the inventive polyimide laminate characteristically
contains Ar
1 in its own general formula (1), wherein the Ar
1 component is at least one kind selected from a group of divalent organic radicals
shown in the following constitutional formula:
[0012] The thermoplastic polyimide polymer used for the inventive polyimide laminate characteristically
contains Ar
2 in its own general formula (1), wherein the Ar
2 component is at least one kind selected from a group of divalent aromatic radicals
shown in the following constitutional formulas:
[0013] The thermoplastic polyimide polymer used for the inventive polyimide laminate characteristically
contains Ar
3 in its own general formula (1), wherein the Ar
3 component is at least one kind selected from a group of quadrivalent aromatic radicals
shown in the following constitutional formula:
[0014] The thermoplastic polyimide polymer used for the inventive polyimide laminate characteristically
contains Ar
4 in its own general formula (1), wherein the Ar
4 component is at least one kind selected from a group of divalent organic radicals
shown in the following constitutional formula:
[0015] The thermoplastic polyimide polymer used for the inventive polyimide laminate characteristically
contains Ar
5 in its own general formula (1), wherein the Ar
5 component is at least one kind selected from a group of quadrivalent aromatic radicals
shown in the following constitutional formulas:
[0016] The thermoplastic polyimide polymer used for the inventive polyimide laminate characteristically
contains Ar
6 in its own general formula (1), wherein the Ar
6 component is at least one kind selected from a group of divalent aromatic radicals
shown in the following constitutional formulas:
[0017] It is an essential of the thermoplastic polyimide film used for the inventive polyimide
laminate that the thermoplastic polyimide polymer specified in any of the above formulas
is formed into film structure.
[0018] It is an essential of the inventive polyimide laminate that the inventive thermoplastic
polyimide polymer specified in any of the above formulas is laminated as of the filmed
form on another film which is subject to exfoliation.
[0019] It is another essential aspect of the inventive polyimide laminate that the inventive
thermoplastic polyimide polymer specified in any of the above formulas is laminated
as of the filmed form on both surfaces of nonthermoplastic polyimide film.
[0020] It is another essential aspect of the inventive polyimide laminate that the laminate
itself comprises a base film layer composed of nonthermoplastic polyimide polymer,
an adhesive-agent layer composed of any of the above-specified inventive thermoplastic
polyimide polymers, and a conductive layer composed of electrically conductive material.
[0021] It is an essential aspect of the inventive method of manufacturing the inventive
polyimide laminate that a base film layer composed of nonthermoplastic polyimide polymer
is initially coated with the solution of a precursor of any of the above specified
thermoplastic polyimide polymers, and then, after executing a drying process and an
imidizing process, the yielded thermoplastic polyimide layer is superposed with a
conductive layer thereon, and finally, the superposed layers are thermally treated
and pressurized to eventually yield the inventive polyimide laminate.
[0022] It is another aspect of the inventive method of manufacturing the inventive polyimide
laminate that a base film composed of nonthermoplastic polyimide polymer is preferably
sequentially superposed with a film composed of any of the above-specified thermoplastic
polyimide polymers and a conductive layer thereon, and then, the superposed layers
are thermally treated and pressurized to eventually yield the inventive polyamide
laminate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023]
Fig. 1 is an explanation of the inventive method of bonding a cover-lay film adhered
with the inventive cover-lay adhesive agent onto a flexible printed circuit board,
wherein (a), (b), and (c) respectively exemplify sectional views of stepwise processes;
and
Fig. 2 is an explanation of the inventive method of bonding a cover-lay film composed
of the inventive thermoplastic polyimide polymer onto a flexible printed circuit board,
wherein (a), (b), and (c) respectively exemplify sectional views of stepwise processes.
OPTIMAL FORM FOR EMBODYING THE INVENTION
[0024] Composition of the improved thermoplastic polyimide polymer, thermoplastic polyimide
film, and inventive polyimide laminate, and the method of manufacturing the polyimide
laminate according to the invention are described below.
[0025] First, the method of formulating solution of polyamide-acid polymer as a precursor
of the thermoplastic polyimide polymer used for the inventive polyimide laminate is
described below. Initially, diamine represented by general formula (2) shown below
is dissolved or diffused in organic solvent in inert gas atmosphere such as argon
or nitrogen, wherein Ar
7 shown in general formula (2) designates a divalent organic radical.
H
2 N - Ar
7 - N H
2 (2)
[0026] Next, only ester-acid dianhydride represented by general formula (3) shown below
(in which Ar
8 designates a divalent organic radical) or a mixture of the ester-acid dianhydride
and at least one kind of organic tetracarbonic acid dianhydride represented by general
formula (4) shown below (in which Ar
9 designates a quadrivalent organic radical) is added to the above diamine solution
in a state in which the above mixture remains solid or being dissolved in organic
solvent, and finally, polyamide-acid polymer solution being a precursor of the thermoplastic
polyimide polymer used for the polyimide laminate is produced.
[0027] The inventive method of formulating polyamide-acid polymer solution being a precursor
of the other thermoplastic polyimide polymer used for the inventive polyimide laminate
is executed according to the sequential steps described below. Initially, only ester
diamine represented by general formula (5) shown below or a mixture of this ester
diamine and at least one kind of diamine represented by the above-identified general
formula (2) is dissolved or diffused in organic solvent in inert gas atmosphere such
as argon or nitrogen, wherein Ar
10 shown in general formula (5) designates a divalent organic radical.
[0028] Next, only ester-acid dianhydride represented by the above identified general formula
(3) or a mixture of this ester acid dianhydride and at least one kind of organic tetracarbonic
acid dianhydride represented by the above-identified general formula (4) or a mixture
of these ester acid dianhydrides and organic tetracarbonic acid dianhydride is added
to the above diamine solution in a state in which said mixture remains solid or being
dissolved in organic solvent, and finally, the novel polyamide-acid polymer solution
being a precursor of the thermoplastic polyimide polymer used for the inventive polyimide
laminate is produced.
[0029] While the above reaction is underway, it is also practicable for the inventive art
to execute those sequential processes described below in such a way inverse from the
above processes. Initially, fresh solution of ester-acid dianhydride represented by
the above-identified general formula (3) or fresh solution of at least one kind of
organic tetracarbonic acid dianhydride represented by the above-identified general
formula (4) or fresh solution of a mixture of these ester-acid dianhydrides and organic
tetracarbonic dianhydride is prepared. Next, only ester diamine represented by the
above-identified general formula (5) or at least one kind of diamine represented by
the above-identified general formula (2) or a mixture of this ester diamine and at
least one kind of diamine represented by the above-identified general formula (2)
is added to the above fresh solution in a state in which said mixture remains solid
or being dissolved in organic solvent or in slurry condition.
[0030] The above reaction should be executed in a temperature ranging from -10 ° C. to a
maximum of 50° C., preferably in a range from -5° C. to a maximum of 20° C. The above
reaction should further be executed within a period ranging from a half hour to a
maximum of 3 hours. As a result of the execution of the above reactions, the novel
polyamide-acid polymer being a precursor of the thermoplastic polyimide polymer represented
by general formula (1) shown below which is used for the inventive polyimide laminate
can properly be yielded.
[0031] In order to properly yield the thermoplastic polyimide polymer used for the inventive
polyimide laminate from the above-exemplified polyamide-acid polymer solution being
a precursor thereof, it is suggested that a method to thermally and/or chemically
dehydrate and cyclize.
[0032] Next, a typical method of producing thermoplastic polyimide film composed of thermoplastic
polyimide polymer is exemplified below. When executing a method to thermally imidize
the thermoplastic polyimide polymer, initially, the solution of the above-identified
polyamide-acid polymer is formed into film on a supporting body such as a supporting
plate, an organic film including PET, a drum or an endless belt by way of flow or
coating with the solution. After a drying process, a self-supporting film is generated.
It is desired that the drying process be executed at a temperature below 150° C. for
about 5 through 90 minutes. Next, the film is further heated and dried until fully
being imidized before eventually producing a novel thermoplastic polyimide film consisting
of thermoplastic polyimide polymer. Optimum heating temperature ranges from 150° C.
to a maximum of 350° C. In particular, it is desired that the heating process be executed
at a temperature ranging from 250 ° C. to 300° C. Although there is no restriction
on the speed of raising temperature during the drying process, it is desired that
the temperature be gradually raised until reaching the above suggested range. Duration
of the heating process depends on the film thickness and the maximum temperature available.
However, it is generally desired that the heating be effected for a period of 10 seconds
up to 10 minutes after reaching the maximum temperature. When heating a self-supporting
film, it is suggested that the film be stripped off from the supporting base and then
heat the stripped film by securing edges. This leads to the generation of satisfactory
polymer containing negligible linear expansion coefficient, and thus this method is
practically preferred.
[0033] The method to chemically imidize polyamide-acid polymer solution is executed by initially
adding more than stoichiometric amount of dehydrating agent and tertiary amine corresponding
to catalytic amount to the polyamide-acid polymer followed by a treatment in the same
way as is done for thermal dehydration before eventually forming desired thermoplastic
polyimide film.
[0034] The chemically imidizing process provides greater mechanical strength and less linear
expansion coefficient for polyimide than the thermally imidizing process. In many
cases, the chemically imidizing process and the thermally imidizing process are conjunctionally
used.
[0035] As a result of imidizing the above polyamide-acid polymer by applying the thermally
imidizing and/or the chemically imidizing processes, the thermoplastic polyimide polymer
represented by the above-identified general formula (1) is yielded, and yet, the thermoplastic
polyimide film composed of the thermoplastic polyimide polymer is produced by executing
the above described chemical and/or thermal imidizing method.
[0036] Ester-acid dianhydrides irrespective of structure may be used for sufficing the ester-acid
dianhydride represented by the above identified general formula (3) available for
the invention. It is desired that the Ar
8 radical shown in the above general formula (3) be of divalent organic radical. Constitutional
formulas of the Ar
8 radical are exemplified below.
More particularly, in order to proportionate a variety of characteristics, it is
preferred that the main constituents of the Ar
8 radical be of the following:
[0037] Ester diamines irrespective of the structure may be used for sufficing the ester
diamine represented by the above-identified general formula (5). However, it is desired
that the Ar
10 radical shown in the above general formula (5) be of divalent organic radical. Constitutional
formulas of the Ar
10 radical are exemplified below.
More particularly, in order to proportionate a variety of characteristics, it is
preferred that the main constituents be of the following:
[0038] Organic tetracarbonic-acid dianhydrides irrespective of the structure may be used
for sufficing the organic tetracarbonic-acid dianhydride available for the invention.
However, the Ar
9 radical shown in the above-identified general formula (4) is of quadrivalent organic
radical, and yet, it is preferred that the Ar
9 radical be of aromatic radical in particular. Constitutional formulas of the Ar
9 radical are exemplified below.
These organic tetracarbonic-acid dianhydrides may be used on a single base or by
way of combining two or more than two of them with each other. More particularly,
in order to proportionate a variety of characteristics, it is preferred that at least
more than one kind of the above-exemplified constitutional formulas be of main constituent.
[0039] Substantially, insofar as being a divalent organic radical, any kind of divalent
organic radical may be used for sufficing the Ar
7 component contained in diamine compound represented by the above-identified general
formula (2). However, those aromatic radicals exemplified below are particularly suited
for use.
[0040] More particularly, it is preferred that available aromatic radical mainly consists
of at least more than one kind of those constitutional formulas exemplified below.
[0041] Those repeating numbers l, m, and n, per block unit present in the thermoplastic
polyimide polymer represented in the above identified general formula (1) are respectively
positive integers of 0 or 1 or more than 1. The sum of the repeating numbers l and
m should be one or more than one. In particular, any of these repeating numbers l,
m, and n, should preferably be 15 or less than 15. This is because, if the repeating
number n ever exceeds 15 times the sum of the repeating numbers l and m, it will cause
the ratio of copolymerization to become defective to result in the minimized effect
of polymerization. More particularly, this is because actual adhesive property under
low temperature cannot properly be identified. It is admissible that those units each
containing different values of the repeating numbers l, m, and n, may be present in
each molecule of polymers. In particular, it is desired that the values of these repeating
numbers l, m, and n, be constant.
[0042] It is also admissible that repeating number t in a block shown in the above general
formula (1) be of positive integer of one or more than one. Although there is no restriction
on the molecular weight of the inventive polyimide polymer in particular, in order
to securely maintain the strength of the yielded polyimide polymer, it is desired
that the polyimide polymer be provided with more than 10000 of mean molecular weight
numerically.
[0043] In many cases, difficulty is involved in the direct measurement of molecular weight
of polyimide polymer. In place of the direct measurement, the molecular weight of
polyimide polymer is inferentially measured via an indirect measuring method. For
instance, when polyimide polymer is synthesized from polyamide acid, a specific value
corresponding to the molecular weight of polyamide acid polymer is determined to be
the molecular weight of polyimide polymer.
[0044] Those organic solvents exemplified below are usable for generating the productive
reaction of polyimide-acid polymer solution, for example, including the following;
sulfoxide solvent such as dimethyl sulfoxide or diethyl sulfoxide, formamide solvent
such as N, N-dimethyl formamide or N, N-diethyl formamide, or acetoamide solvent such
as N, N-dimethyl acetoamide or N,N-diethyl acetoamide. These organic solvents may
be used on an individual base or by way of mixing plural kinds with each other. The
above-cited polar solvents may also be mixed with any of those non-solvents of polyamid-acid
polymer such as acetone, methanol, ethanol, isopropanol,or benzene methyl-cellosolve,
for example.
[0045] By virtue of novel constitutional features described above, the thermoplastic polyimide
polymer used for the inventive polyimide laminate has evident glass transition point
between 100° C. and 250° C. Accordingly, polyimide film and copper foil or polyimide
films can easily be bonded with each other merely by laminating them at a temperature
close to the glass transition point, and yet, the thermoplastic polyimide film used
for the inventive polyimide laminate yields satisfactory adhesive property under low
temperature. It was also proven that the thermoplastic polyimide film used for the
inventive polyimide laminate merely exhibited about 1% of hygroscopic degree after
being immersed in pure water at 20° C. for 24 consecutive hours. Furthermore, it was
also confirmed that the thermoplastic polyimide film used for the inventive polyimide
laminate exhibited satisfactory resistivity against radioactive rays.
[0046] Accordingly, in place of conventional acrylic or epoxy adhesive agent, the thermoplastic
polyimide film used for the inventive polyimide laminate is ideally usable for composing
flexible copper-coated laminates and bilateral adhesive sheets or adhesive-agent layers
for cover-lay films. Next, fields of application of the thermoplastic polyimide polymer
used for the inventive polyimide laminate are described below.
[0047] The thermoplastic polyimide polymer used for the inventive polyimide laminate is
practically usable by thermally melting it or by way of imidizing it after being coated
on a bonding object as of the state of polyamide-acid polymer solution being a precursor
of the above polyimide polymer. Furthermore, after being formed into thermoplastic
polyimide film, the thermoplastic polyimide film used for the inventive polyimide
laminate can serve as adhesive film. To suffice those uses cited above, supply can
be effected as of polyimide film, thus providing handling convenience.
[0048] Characteristically, since the thermoplastic polyimide film used for the inventive
polyimide laminate conceptually comprises films and sheet forms, and yet, since the
polyimide film used for the inventive polyimide laminate exhibits distinctly low hygroscopic
property, not only for an adhesive-agent film, but it also ideally serves as a base
film of a cover-lay film of flexible copper-coated laminates. Furthermore, since the
thermoplastic polyimide film used for the inventive polyimide laminate is highly resistant
to radioactive rays, it is also effectively applicable to a variety of apparatuses
potentially being affected by radioactive rays.
[0049] Furthermore, the inventive thermoplastic polyimide laminate comprising adhesive agent
layers composed of film-forming layers of the thermoplastic polyimide polymer being
laminated on both surfaces of nonthermoplastic polyimide film serving as a base film
is effectively applicable to a bilateral or single-surface polyimide adhesive sheet
containing adhesive-agent layer consisting of the thermoplastic polyimide polymer
layers. Furthermore, the inventive polyimide laminate is also usable for composing
a flexible copper-coated laminate by way of bonding it with copper foil. Incidentally,
bilateral adhesive sheets containing adhesive-agent layers on both surfaces of base
film are suitably used for the base material for composing flexible printed circuit
boards which have been multilayered in recent years. In addition, bilateral adhesive
sheets are also usable for the cover-lay film adhered with adhesive agent.
[0050] The inventive polyimide laminate can easily be manufactured by initially superposing
the thermoplastic polyimide polymer film used for the inventive polyimide laminate
on both surfaces of a basic polyimide film such as "APICAL" (a product and a registered
trade name of Kanegafuchi Chemical Industrial Co., Ltd.) followed by the execution
of a thermal bonding process.
[0051] As another method of manufacturing the inventive polyimide laminate, it is also practicable
to initially dissolve the thermoplastic polyimide polymer used for the inventive polyimide
laminate via a heating process and then directly coat the melted polyimide polymer
on both surfaces of the basic polyimide film.
[0052] It is also practicable for the production of the inventive polyimide laminate to
initially spread polyamide-acid polymer solution being a precursor of the thermoplastic
polyimide polymer used for the inventive polyimide laminate on a basic polyimide film,
and then dry the spread solution before eventually imidizing the dried polymer content.
[0053] When providing the thermoplastic polyimide polymer layers on both surfaces of a base
film, after completing the above processes, polyamide-acid polymer solution is spread
over on the other surface of the base film, and then, after completing a drying process,
the dried polymer content is imidized. It is also practicable to simultaneously spread
polyamide-acid polymer solution over both surfaces of the basic polyimide film before
imidizing the spread solution. In addition, it is also practicable to initially spread
polyamide-acid polymer solution over the basic polyimide film, and then, after completing
a drying process, polyimide-acid polymer solution is spread over the other surface
of the base film, and then, after completing a drying process, polyamide-acid polymer
films on both surfaces of the base film is eventually imidized.
[0054] The inventive polyimide laminate completed from the above sequential processes characteristically
contains outstanding thermal resistant property, adhesive property under low temperature,
workability, and low hygroscopic property. Copper foil can securely be bonded to the
inventive polyimide laminate by laminating superposed copper foils at a temperature
close to the glass transition point (from 100° C. to 250° C.) of thermoplastic polyimide
polymer layers which make up adhesive-agent layers, thus making it possible to easily
produce flexible copper-coated laminates. In particular, bilateral adhesive polyimide
sheets are ideally suited for the production of the flexible copper-coated laminates
capable of satisfying industrial demand for achieving the multi-layering of flexible
printed circuit boards.
[0055] Not only using the novel polyimide laminates described above, but the flexible copper-coated
laminates can also be manufactured by sequentially executing those processes including
the superposition of a basic nonthermoplastic polyimide film, the thermoplastic polyimide
film serving as the adhesive-agent film, and conductive layers such as copper foils
followed by the execution of a thermal bonding process.
[0056] Although aluminium, iron, nickel, and other conductive materials may be used for
composing conductive layers, copper foil is particularly suited for use.
[0057] The thermoplastic polyimide film and the polyimide laminate are ideally suited for
composing adhesive-agent layers and the base film of a flexible copper-coated laminate.
The flexible copper-coated laminate and the bilateral adhesive polyimide sheet produced
by the execution of the above-exemplified inventive art conjunctionally contain distinctive
thermal resistant property, adhesive property under low temperature, workability,
low hygroscopic property. In particular, the inventive bilateral adhesive polyimide
sheet is effective for producing bilateral flexible printed circuit boards and multiple-layer
printed circuit boards.
[0058] Characteristically, since the inventive polyimide laminate totally being composed
of polyimide is compatible with alkaline etching process, perforation can easily be
achieved. Accordingly, in the course of manufacturing flexible printed circuit boards,
after completing an etching process against copper foil of flexible copper-coated
laminates, polyimide can be perforated via an alkaline etching process to facilitate
the production of flexible printed circuit boards. Furthermore, since the inventive
polyimide laminate merely exhibits about 1% of low hygroscopic degree after being
immersed in pure water at 20 ° C. for 24 consecutive hours, the inventive polyimide
laminate is optimal for the base film of flexible printed circuit boards.
In addition, the inventive polyimide laminate is evidentially resistant against radioactive
rays without incurring transmutation nor discoloration from irradiation of radioactive
rays. Because of this distinctive resistivity, the inventive polyimide laminate can
usefully be utilized for such apparatuses potentially being affected by radioactive
rays. There is no limit on other uses.
[0059] Furthermore, the thermoplastic polyimide film and the inventive polyimide laminate
can effectively be used for composing cover-lay adhesive agent and cover-lay films.
The thermoplastic polyimide film used for the inventive polyimide laminate can practically
be utilized for the cover-lay adhesive agent based on those sequential steps described
below.
[0060] The following description with respect to the Figures is useful for understanding
the present invention, but does not constitute an embodiment thereof although the
methods described below can also applied to the present invention.
[0061] As is exemplified in Fig. 1(a), initially, a polyimide film 10 composed of nonthermoplastic
polyimide polymer such as "APICAL" (a product and a registered trade name of Kanegafuchi
Chemical Industrial Co., Ltd.), another film 12 composed of the thermoplastic polyimide
polymer, are superposed on the conductive surface of a flexible printed circuit board
16 accommodating a circuit 14 thereon. Next, as is exemplified in Fig. 1(b), the above
superposed components are thermally bonded together to easily achieve adhesion. Next,
as is exemplified in Fig. 1(c), initially, a resist film 18 is formed on a predetermined
position of the polyimide film 10 by applying a photolithographic process or a screen
printing process. Next, a plurality of through-holes 20 are formed through the polyimide
film 10 and the other film 12 via an alkaline etching process. As is exemplified above,
by executing a perforation process after adhering the polyimide film 10 serving as
a cover-lay film onto the flexible printed circuit board 16 with the other film 12
functioning as cover-lay adhesive agent, a flexible printed circuit board easily adhered
with a cover-lay film can be manufactured.
[0062] The polyimide laminate manufactured via the above exemplified method can be used
as a cover-lay film adhered with cover-lay adhesive agent. Accordingly, the cover-lay
film can properly be adhered with a perforated cover film via an alkaline etching
process after thermally bonding the adhesive surface and the conductive surface of
the flexible printed circuit board previously being laminated with each other, thus
easily manufacturing such a flexible printed circuit board properly being adhered
with a cover-lay film.
[0063] As was described above, although it is practicable to adhere a cover-lay film composed
of nonthermoplastic polyimide polymer onto a flexible printed circuit board with cover-lay
adhesive agent, since the above-described thermoplastic polyimide polymer merely exhibits
about 1% of low hygroscopic degree after being immersed in pure water at 20 ° C. for
24 hours, the film composed of the thermoplastic polyimide polymer functioning as
cover-lay adhesive agent may be available for the cover-lay film.
[0064] For instance, as is exemplified in Fig. 2, initially, polyamide acid being a precursor
of the thermoplastic polyimide polymer functioning as cover-lay adhesive agent is
fluidly spread over an exfoliatable paper or an exfoliatable film 22 such as a PET
film for coating it, and then, the coated polyimide acid is imidized before eventually
laminating a cover-lay film 24 composed of the thermoplastic polyimide polymer on
the exfoliatable film 22. Furthermore, as is exemplified in Fig. 2(a) and (b), the
cover-lay film 24 is then thermally bonded with the conductive surface of a flexible
printed circuit board 16 accommodating a circuit 14 formed thereon, and then, the
exfoliatable film 22 is stripped off. Next, as is exemplified in Fig. 2(c), a plurality
of through-holes 26 are formed in the cover-lay film 24 via an alkaline etching process
before easily forming up the flexible printed circuit board 16 adhered with the cover-lay
film 24.
[0065] It is also practicable to initially form a cover-lay film from the thermoplastic
polyimide polymer substantially being cover-lay adhesive agent, and then, the cover-lay
film is thermally adhered to the flexible printed circuit board 16 via an exfoliatable
film before eventually removing the exfoliatable film.
[0066] The cover-lay adhesive agent or film produced from the above methods is totally composed
of polyimide. Since an alkaline etching process can be effected against polyimide,
perforation can easily be executed after the adhesion of polyimide cover-lay film
to the flexible printed circuit board. Accordingly, this method not only dispenses
with a preliminary positioning work otherwise needed for any conventional method,
but the method can also simplify the manufacturing processes by way of executing the
positioning work simultaneous with the execution of an alkaline etching of the base
film of the flexible printed circuit board.
[0067] As is evident from the above description, the thermoplastic polyimide film is optimally
usable for the cover-lay adhesive agent which is inserted between a cover-lay film
composed of non-thermoplastic polyimide film and a flexible printed circuit board.
In addition, the polyimide laminate comprising the previously formed laminate of nonthermoplastic
polyimide film and the thermoplastic polyimide film can be used to serve as a cover-lay
film adhered with cover-lay adhesive agent. Furthermore, the thermoplastic polyimide
film itself may serve as a cover-lay film. There is no limit on other uses of the
thermoplastic polyimide film. The inventive polyimide laminate will be described below
with reference to Examples.
[0068] The above description has solely referred to the thermoplastic polyimide polymer,
the inventive thermoplastic polyimide film, both used for the inventive polyimide
laminate, and exemplified method of manufacturing the inventive polyimide laminate.
[0069] The invention is further described by way of examples. It should be understood however
that the scope of the invention as defined by the claims is by no means limited to
the following examples.
[0070] The Reference Examples do not fall under the scope of the claims.
Reference EXAMPLE 1:
[0071] Initially, 16.9 grams of 2,2-bis [4-(4-aminophenoxy)phenyl] propane (hereinafter
merely referred to as BAPP) and 25.4 grams of dimethyl formamide (hereinafter merely
referred to as DMF) were respectively sampled in a female flask (1) having 50ml of
capacity. Next, using a stirrer, the sampled BAPP and DMF were stirred until fully
being dissolved. Separately, 1.0 gram of BAPP and 10.0 grams of DMF were respectively
put in another female flask (2) having 50ml of capacity, and then, both samples were
also stirred until fully being dissolved therein. Separately, 11.9 grams of 2,2-bis
(4-hydroxyphenyl) propane dibenzoate-3,3'4,4'-tetracarboxylic acid dianhydride (hereinafter
merely referred to as ESDA), 4.5 grams of pyromellit acid dianhydride (hereinafter
merely referred to as PMDA), and 25.0 grams of DMF, were respectively put in a 500ml-capacity
three-necked flask equipped with a stirrer. While being cooled off in ice water and
replacing atmosphere in the flask with nitrogen, sampled chemical constituents were
stirred until fully being dissolved therein.
[0072] Next, while stirring the previously prepared BAPP solution in the 50ml-capacity female
flask (1), the stirred BAPP solution was quickly poured into the 500ml-capacity three-necked
flask, and then the mixed solution was aged for a half hour while continuously stirring
it. Next, while watching the viscosity of the mixed solution in the 500ml-capacity
three-necked flask, the previously prepared BAPP solution in the 50ml-capacity female
flask (2) was gradually put in the three-necked flask. After reaching the maximum
viscosity, the transfer of the BAPP solution from the 50ml-capacity female flask (2)
to the 500ml-capacity three-necked flask was terminated, and then, the mixed solution
was aged for an hour while continuously being stirred in the three-necked flask. Next,
78.2 grams of DMF was added to the mixed solution, and then, after fully stirring
the mixed solution, polyamide acid polymer solution was eventually yielded.
[0073] Next, polyimide film (a product of Kanegafuchi Chemical Industrial Co., Ltd.) was
superficially coated with the yielded polyamide polymer solution. After being heated
at 80° C. for 25 minutes, the polyamide polymer solution-coated film was further heated
at 150° C., 200° C., 250° C., and 300° C. for 5 minutes each to effectuate imidation
before eventually yielding polyimide laminate comprising the thermoplastic polyimide
polymer layers.
[0074] Next, based on the TMA and the ASTM D-570, inventors checked the glass transition
point (° C.) and the hygroscopic degree (%) of the inventive thermoplastic polyimide
polymer from the yielded polyimide laminate. In addition, in order to check adhesive
property of the inventive polyimide laminate, based on JIS K6481, inventors checked
the peeling strength (kg/cm) of a flexible copper-coated laminate manufactured from
the lamination of thermoplastic polimide polymer layer surface of the yielded polyimide
laminate and a copper foil having 35 µm of thickness by laminating them at 300° C.
and 2.2 cm/min. of speed. The test results are presented in Table 1 shown below.
TABLE 1
|
Glass transition point (°C) |
Peeling strength (kg/cm) |
Hygroscopic degree (%) |
Reference Example 1 |
222 |
2.0 |
1.13 |
Reference Example 2 |
205 |
1.0 |
0.90 |
Reference Example 3 |
122 |
1.4 |
0.95 |
Reference Example 4 |
130 |
2.0 |
1.13 |
Reference Example 5 |
185 |
1.6 |
1.45 |
Example |
229 |
1.1 |
1.12 |
Comparative example 1 |
238 |
No adhesion |
1.98 |
Comparative example 2 |
238 |
0.3 |
1.98 |
Comparative example 3 |
178 |
No adhesion |
1.98 |
Reference EXAMPLE 2
[0075] Initially, 1.0 gram of ESDA and 10.0 grams of DMF were respectively sampled in a
50ml-capacity female flask, which were then sufficiently stirred with a stirrer until
fully being dissolved.
[0076] Independently, 12.9 grams of 2,2-bis(4-aminobenzyloxyphenyl) propane (hereinafter
merely referred to as BABPP) and 38.7 grams of DMF were respectively sampled in a
500ml-capacity three-necked flask equipped with a stirrer. Both samples were then
sufficiently stirred until fully being dissolved while replacing atmosphere in the
flask with nitrogen.
[0077] Next, 14.9 grams of ESDA was sampled in a 100ml-capacity eggplant flask and then
added to the dissolved BABPP solution as of solid form. Next, availing of 37.7 grams
of DMF, residual ESDA adhered to the wall surface of the 100ml-capacity eggplant flask
was transferred to the 500ml-capacity three-necked flask. After aging the mixed solution
for about an hour while continuously stirring it, the ESDA solution in the 50ml-capacity
female flask was gradually put in the 500ml-capacity three-necked flask while watching
the viscosity of the solution in the three-necked flask. After reaching the maximum
viscosity, the supply of the ESDA solution was terminated. After aging the mixed solution
for an hour while continuously stirring it, polyamide acid polymer solution was eventually
yielded.
[0078] Next, a PET film was superficially coated with the yielded polyamide-acid polymer
solution, and then the coated film was thermally treated at 80° C. for 25 minutes
before fully being dried to such an extent capable of retaining self-supporting solidness.
Next, polyamide-acid polymer film was stripped off from the PET film and then secured
to a metallic supporter. The secured polyamide acid polymer film was then sequentially
heated at 150 ° C., 200° C., 250° C., and 300° C., for 5 minutes each until fully
being imidized, and then, thermoplastic polyimide polymer film was eventually yielded.
[0079] Then, the yielded thermoplastic polyimide polymer film was superposed on a polyimide
film "APICAL" (a product and a registered trade name of Kanegafuchi Chemical Industrial
Co., Ltd.) and a copper foil having 35 µm of thickness, which were then laminated
altogether at 300 ° C. and 2.2cm/min. of speed. Finally, a flexible copper-coated
laminate was yielded.
[0080] In order to check physical properties of the yielded flexible copper-coated laminate,
as was done for the Reference Example 1, inventors checked the glass transition point
(° C.) and the hygroscopic degree (%) of the thermoplastic polyimide polymer and the
peeling strength (kg/cm) of the flexible copper-coated laminate. The test results
are also shown in Table 1.
Reference EXAMPLE 3
[0081] Initially, 1.0 gram of ethylene glycol bis-trimellitic acid dianhydride (hereinafter
merely referred to as TMEG) and 10.0 grams of dimethyl formamide (hereinafter merely
referred to as DMF) were respectively sampled in a 50ml-capacity female flask, which
were then stirred therein with a stirrer before fully being dissolved. Independently,
22.7 grams of 2,2-bis (4-aminobenzyloxyphenyl) propane (hereinafter merely referred
to as BABPP) and 68.1 grams of DMF were respectively sampled in a 500ml-capacity three-necked
flask, which were then stirred while replacing atmosphere in the flask with nitrogen
until fully being dissolved therein. Next, 19.0 grams of TMEG was sampled in a 100ml-capacity
eggplant flask and then added to the BABPP solution as of solid form. Next, residual
TMEG adhered to the wall surface of the 100ml-capacity eggplant flask was put in the
500ml-capacity three-necked flask via the aid of 21.5 grams of DMF. After aging the
mixed solution for about an hour while continuously stirring it, the TMEG solution
stored in the 50ml-capacity female flask was gradually put in the 500ml-capacity three-necked
flask while watching the viscosity in the three-necked flask. After reaching the maximum
viscosity, the supply of TMEG solution was terminated. Next, the mixed solution was
aged for an hour while continuously being stirred in the three-necked flask, and finally,
polyamide-acid polymer solution was yielded.
[0082] Before imidizing the yielded polyamide-acid polymer solution, the polyamide-acid
polymer solution was formed into film by executing those sequential processes described
below. After completing a laminated film, inventors checked physical properties. Initially,
2.0 grams of isoquinoline and 20.0 grams of acetic acid anhydride were respectively
sampled in a 100ml-capacity female flask, which were then sufficiently stirred. Next,
the prepared solution was added to the prepared polyamide-acid solution, and then,
the mixed solution was sufficiently stirred for 2 minutes before fully extracting
air therefrom. Next, a PET film was coated with the air-extracted solution and then
thermally treated at 80° C. for 25 minutes. After stripping off the PET film, the
mixed components were thermally treated by way of continuously raising temperature
from 150° C. to 200° C., and then further heated for 10 minutes before being imidized,
and finally, film-form thermoplastic polyimide was yielded.
[0083] As was done for the Reference Example 1, inventors checked the glass transition point
(° C.) and the hygroscopic degree (%) of the yielded thermoplastic polyimide film.
Furthermore, in order to check adhesive property thereof, a polyimide film "APICAL"
(a product and a registered trade name of Kanegafuchi Chemical Industrial Co., Ltd.),
the yielded thermoplastic polyimide film, and an exfoliatable paper, were superposed
before being laminated together at 150 ° C. and 2.2cm/min. of speed to produce a polyimide
lamination, and further, an exfoliatable paper was exfoliated from the polyimide lamination
and instead of the exfoliatable paper, copper foil was applied, and finally, a flexible
copper-coated laminated board was completed by being laminated at 150 °C. and 2.2cm/min.
of speed. As was done for the Reference Example 1, inventors checked the peeling strength
(kg/cm) of the completed flexible copper-coated laminated board. The test results
are also shown in Table 1.
Reference EXAMPLE 4
[0084] Except for the use of 13.3 grams of 1,3-bis (4-aminophenoxy) -2,2-dimethyl propane
in place of BABPP, in the same way as was done for the Example 3, film-form thermoplastic
polyimide was yielded for the Example 4. Furthermore, as was done for the Example
3, after manufacturing a polyimide laminate, a flexible copper-coated laminate was
eventually yielded. In the same way as was done for the Example 1, inventors checked
the glass transition point, the hygroscopic degree, and the peeling strength of the
yielded thermoplastic polyimide film and flexible copper-coated laminate. The test
results are shown in Table 1.
Reference EXAMPLE 5
[0085] Polyamide-acid polymer solution was yielded by the effect of copolymerization which
was executed by adding 30ml of DMF, 22.7 grams of BABPP, and 10.6 grams of PMDA, to
the polyamide-acid polymer solution yielded via the Reference Example 3. As was done
for the Reference Example 3, the yielded polyamide-acid polymer solution was imidized
before making up a polyimide laminate, and finally, a flexible copper-coated laminated
board was completed. In the same way as was done for the Reference Example 1, inventors
checked the glass transition point, the hygroscopic degree, and the peeling strength
of the manufactured thermoplastic polyimide film and flexible copper-coated laminated
board. The test results are shown in Table 1.
EXAMPLE
[0086] Initially, 1.0 gram of PMDA and 10.0 grams of DMF were respectively sampled in a
50ml-capacity female flask, which were then sufficiently stirred with a stirrer until
fully being dissolved. Independently, 23.3 grams of BABPP and 50.0 grams of DMF were
sampled in a 500ml-capacity three-necked flask equipped with a stirrer, which were
then stirred while replacing atmosphere in the flask with nitrogen until fully being
dissolved. Next, 9.9 grams of PMDA was sampled in a 100ml-capacity eggplant flask,
which was then added to the prepared BABPP solution as of solid form. Next, residual
PMDA adhered to the wall surface of the 100ml-capacity eggplant flask was dissolved
with 19.8 grams of DMF and then put in the 500ml-capacity three-necked flask. After
aging the mixed solution for about an hour while continuously stirring it, the PMDA
solution prepared in the 50ml-capacity female flask was gradually transferred to the
three-necked flask while paying attention to the viscosity of the solution stored
in the three-necked flask. After reaching the maximum viscosity, the supply of the
PMDA solution was terminated. After aging the mixed solution for an hour while continuously
stirring it, polyamide-acid polymer solution was eventually yielded.
[0087] Next, a PET film was superficially coated with the yielded polyamide-acid polymer
solution, and then the coated solution was thermally treated at 80° C. for 25 minutes.
Then, the thermally treated polyamide-acid polymer content was stripped off from the
PET film and then secured to a metallic supporter, which was then sequentially heated
at 150° C., 200° C., 250° C., and 300° C., for 5 minutes each to implement imidation,
and finally, thermoplastic polyimide film was yielded. Next, the thermoplastic polyimide
polymer films yielded from the above processes were superposed on both surfaces of
a polyimide film before being laminated therewith at 300° C. and 2.2cm/min. of speed.
Finally the inventive polyimide laminate was completed.
[0088] As was done for the Reference Example 1, inventors checked the glass transition point
and the hygroscopic degree of the yielded polyimide laminate. Furthermore, in order
to check the adhesive property of the polyimide laminate, copper foils each having
35 µm of thickness were superposed on both surfaces of the yielded polyimide laminate
and then laminated together at 300° C. and 2.2cm/min. of speed before completing a
flexible copper-coated laminated board. As was done for the Reference Example 1, inventors
checked the peeling strength of the completed flexible copper-coated laminated board.
The test results are also shown in Table 1.
[0089] In addition, inventors also tested all the flexible copper-coated laminated boards
yielded from the above-described Reference Examples 1 to 5 and the inventive Example
to check their resistivity to radioactive rays via irradiation of 5MGy using electronic
cables having 2MeV of capacity. In consequence, neither discoloration of any of the
laminated films nor degradation of used material was generated.
Comparative Example 1
[0090] Initially, 1.94 gram of 3,3' 4,4'-benzophenone tetracarboxylic dianhydride (hereinafter
merely referred to as BTDA) and 30.0 grams of DMF were sampled in a 50ml-capacity
female flask and then fully dissolved therein. Independently, 51.8 grams of BAPP and
310.0 grams of DMF were sampled in a 500ml-capacity three-necked flask equipped with
a stirrer. While cooling off the three-necked flask with ice water and replacing atmosphere
of this flask with nitrogen, sampled chemicals were stirred well until fully being
dissolved. Independently, 38.8 grams of BTDA was sampled in a 100ml-capacity eggplant
flask, which was then added to the BAPP solution as of solid form. Next, residual
BTDA adhered to the wall surface of the 100ml-capacity eggplant flask was fluidly
transferred to the 500ml-capacity three-necked flask via the aid of 10.0 grams of
DMF. After aging the mixed solution stored in the three-necked flask for about an
hour while continuously stirring it, while paying attention to the viscosity of the
mixed solution in the three-necked flask, the BTDA solution stored in the 50ml-capacity
female flask was gradually put in the three-necked flask. After reaching the maximum
viscosity, the supply of the BTDA solution was terminated, and then the mixed solution
in the three-necked flask was aged for an hour while continuously being stirred. Next,
DMF was further added to the mixed solution until the total amount of the sample reached
500 grams. After stirring the mixed solution, polyamide-acid polymer solution was
yielded.
[0091] Next, a polyimide film (a product of Kanegafuchi Chemical Industrial Co., Ltd.) was
superficially coated with the yielded polyamide acid polymer solution and then thermally
treated at 80° C. for 25 minutes. Next, the polyamide-acid polymer coated polyimide
film was sequentially heated at 150 ° C., 200° C., 250° C., and 300° C., for 5 minutes
each to implement imidation, and finally, a polyimide laminate incorporating thermoplastic
polyimide polymer layers was yielded.
[0092] As was done for the Reference Example 1, inventors checked the glass transition point
(° C.) and the hygroscopic degree (%) of thermoplastic polyimide polymer of the yielded
polyimide laminate. In order to check the adhesive property of the polyimide laminate,
a copper foil having 35 µm of thickness was superposed on the surface of thermoplastic
polyimide polymer layer of the yielded polyimide laminate before being laminated at
300° C. and 2.2cm/min. of speed. Nevertheless, the copper foil did not adhere to the
surface of thermoplastic polyimide polymer layer. This result is expressed in Table
1. On the other hand, as a result of the testing resistivity of the polyimide laminate
against radioactive rays by irradiating 5MGy via 2MeV electronic cables, it was proved
that neither discoloration of laminated film nor degradation of used material was
generated.
Comparative Example 2
[0093] Using the polyimide laminate yielded from the Comparative Example 1, lamination was
effected between the polyimide laminate and copper foils under a condition different
from the Comparative Example 1. Concretely, as a result of the lamination executed
at 300° C. and 0.3cm/min. of slow speed, copper foils adhered to the thermoplastic
polyimide polymer layers, and thus, flexible copper-coated laminated boards were yielded.
[0094] As was done for the Reference Example 1, inventors checked the peeling strength of
the yielded flexible copper-coated laminated boards. As shown in Table 1, the peeling
strength of the laminated boards was rated to be 0.3kg/cm, thus failing to achieve
sufficient strength.
Comparative Example 3
[0095] In place of the thermoplastic polyimide polymer substantially serving as adhesive
agent, using a conventional epoxy adhesive agent "EPICOAT" 828 (a product of Yuka-Shell
Co., Ltd.), lamination was executed at 150° C. and 2.2cm/min. of speed as was done
for the Reference Example 3 before eventually yielding a flexible copper-coated laminated
board.
[0096] As a result of checking the physical properties of the yielded flexible copper-coated
laminated board as per the method executed for the Reference Example 1, the above-cited
epoxy adhesive agent exhibited 178° C. of glass transition point and 1.98% of hygroscopic
degree. As was done for the Reference Example 1, inventors also checked the peeling
strength of the yielded flexible copper-coated laminated board. Nevertheless, since
the copper foil failed to adhere itself to the thermoplastic polyimide polymer layers,
the peeling strength was not measurable. This result is expressed in Table 1. As a
result of the testing resistivity of the yielded flexible copper-coated laminated
board via irradiation of 5MGy radioactive rays with 2MeV electronic cables, it was
found that the laminated film turned into black.
Industrial applicability of the Invention
[0097] As is evident from the above description, by virtue of utilization of thermoplastic
polyimide polymer expressed by the above-identified general formula (1) for the inventive
polyimide laminate, the invention securely materializes the distinctive thermal resistant
property and adhesive property of the resultant flexible printed circuit boards. The
thermoplastic polyimide polymer for the inventive polyimide laminate is ideally usable
for sufficing adhesive-agent layer needed for manufacturing flexible printed circuit
boards. Actually, because of poor thermal resistant property, any of those conventional
epoxy adhesive agents thus far being used for manufacturing flexible printed circuit
boards failed to activate distinctive thermal resistant property of polyimide film
serving as a base film. On the other hand, in order to properly effect adhesion, any
of those conventional adhesive agents composed of conventional thermoplastic polyimide
polymers obliges manufacturers to execute heating and compressing processes for a
long duration with pressurizing means, thus resulting in extremely poor productivity,
low adhesion, and failure to achieve sufficient adhesive strength of processed objects.
[0098] On the other hand, since the polyimide film consisting of the inventive thermoplastic
polyimide polymer expressed by the above-identified general formula (1) used for the
inventive polyimide laminate is not only quite distinctive in terms of thermal resistant
property and adhesive strength, but it also provides adhesion with sufficient strength
merely by executing a short-period pressurizing process, and accordingly, the polyimide
film serving as a novel adhesive agent used for the inventive polyimide laminate securely
enables manufacturers to properly manufacture flexible copper-coated laminated boards
with improved productivity.
[0099] Furthermore, the inventive polyimide laminate comprising thermoplastic polyimide
polymer layers being laminated on both surfaces of a nonthermoplastic polyimide film
can serve as a bilateral adhesive sheet, and yet, it can also be used for the base
film of a cover-lay film having adhesive-agent layer and a flexible copper-coated
laminated board. The inventive polyimide laminate can properly be perforated via an
alkaline etching process, and thus, when being used as a cover-lay film, after completing
the adhesion of the polyimide laminate to the surface of circuits formed on a flexible
printed circuit board, perforation can easily be executed, thus making it possible
for manufacturers to significantly improve operating efficiency for adhesion of a
cover-lay film.
[0100] Furthermore, since the thermoplastic polyimide polymer used for the inventive polyimide
laminate characteristically exhibits extremely low hygroscopic degree, the thermoplastic
polyimide film formed from this polymer is ideally suited not only for serving as
an adhesive-agent film, but also for serving as the base film or a cover-lay film
of a flexible printed circuit board.
[0101] In particular, the thermoplastic polyimide polymer represented by the above-identified
general formula (1) used for the inventive polyimide laminate has proved to be distinctively
resistant to radioactive rays, and accordingly, such flexible printed circuit boards
made from the inventive polyimide laminate are effectively usable for those apparatuses
potentially being affected by radioactive rays.